The present invention relates to a power and free conveyor system, particularly to a retractable pusher dog for driving rail-guided load carriers or trolleys along a free rail of an overhead power and free conveyor system.
In typical power and free conveyors, a leave in is mounted on a load trolley or trolleys which run on a non-powered free rail. The load carrier is moved by a continuously running power or drive chain by engagement between a drive element or pusher dog on the drive chain and a trolley head on the load carrier or trolley. The drive chain is supported by ball bearing wheels running inside an enclosed powered track. In overhead power and free conveyors, a load supported by the load carrier is suspended below the free rail supporting the load trolleys and the drive chain. The pusher dog extends downward to engage an upwardly extending trolley dog or head or simply the front trolley head of the load carrier. The trolley head may be caused to disengage from the pusher dog to allow the load to coast on a downhill section of the load track, to halt the load for operations thereon, or the like. An efficient conveyor system provides for repeatability, precision and continuous flow of operations.
On many power and free conveyors, the load trolleys incorporate accumulation mechanisms which cause drive disengagement of carriers approaching behind a halted carrier to prevent collisions between the carriers and loads. Examples of such systems are disclosed in U.S. Pat. Nos. 4,073,238 to Knudsen, 4,326,466 to Parry et al., 4,389,944 to Linton et al., and 5,606,915 to Harris. While these systems will prevent damage to the trolleys and the drive chain, the accumulation mechanisms are only activated when one load carrier comes into engagement with another carrier actuating the withdrawal of the trolley dog. These systems are best suited for single rail systems where the load trolley and pusher dog are always in the same horizontal path. A drawback of these systems are increased costs due to the complexity and added components of the actuating means constructed on the trolley. Also, some of the systems require resetting of the trolley dogs after actuation out of engagement with the pusher dog resulting increased downtime and increased labor cost to keep the system operating efficiently. These systems do not contemplate a load trolley entering a branch line where misalignment between a load trolley and pusher dog is possible.
To avoid damage to the drive chain, some systems incorporate drive elements or pusher dogs which can actuate out of engagement with the trolley dog. Examples of such systems are disclosed in U.S. Pat. Nos. 3,623,538, 4,073,237 and 4,885,997 to Wakabayashi, and U.S. Pat. No. 4,004,680 to Warmann. To accomplish the disengagement of the drive element from the trolley dog, modifications must be made to the trolleys and/or rails. These modifications increase the complexity of the system and correspondingly increase the cost of installation. Also, due to the complexity of the multi-component pusher dogs, the systems are exposed to increased points of failure and increased downtimes.
The above-mentioned systems are primarily concerned with preventing damage to the various components of a power and free conveyor caused by a blockage or stoppage of a load trolley on the free rail. The prior art systems do not contemplate the damage that occurs when a load trolley is fed into a powered system in harddog mode and the timing between the two is off. The prior art pusher dogs are usually rigid in normal operation. If a load trolley is fed into a powered system out of synchronization with the pusher dogs of the power chain, the pusher dog comes into contact with the top of the load trolley and can crush the load trolley causing a blockage on the free rail resulting in system downtime. Alternatively, the pusher dog itself could be damaged or, if enough stress is put on the drive chain, the chain could fracture and break.
Additionally, this lack of flexibility of the pusher dog causes conveyor system designers to over-compensate for possible troubled areas, such as making extra wide turns, very gradual declines, etc, which result in overly large systems and increased material costs. Also, due to the rigidity of the pusher dog, the powered rail and free rail must be precisely aligned to prevent contact between the rigid pusher dog and free rail thus avoiding damage to the system. The precise and accurate setup of this type of system will also result in increased installation labor costs.
It is an object of the subject invention to provide a retractable pusher dog which is self-actuating.
It is another object of the subject invention to provide a retractable pusher dog which requires no modifications to the power and free rails or load trolleys.
Another object of the subject invention is to provide a retractable pusher dog which allows automatic feeding of load trolleys from one powered system, in harddog mode, to another without jamming the load trolleys when timing may be off.
It is another object of the subject invention to provide a retractable pusher dog which allows manual feeding of load trolleys onto a powered system in harddog mode without the worry of binding or breaking the trolley.
It is another object of the subject invention to provide a retractable pusher dog with enough flexibility to enable system designers to be more versatile in troubled areas.
A further object of the subject invention is to provide a retractable pusher dog which can be installed on a drive chain without disassembling the drive chain.
It is a further object of the subject invention to provide a retractable pusher dog which can be retrofitted onto many types of existing power and free conveyors.
The above stated objects are met by a new and improved retractable pusher dog. The subject retractable pusher dog comprises a body portion formed from a rectangular cylinder with two body plates spaced parallel from each other along the longitudinal axis of the cylinder. The cylinder further comprises two pairs of parallel walls with one pair of the parallel walls having slots in the direction of the longitudinal axis of the cylinder. The body plates are formed to engage a drive chain of a power and free conveyor system. The body plates are positioned to close a first end of the rectangular cylinder. A spring and pusher member are disposed within the cylinder. The pusher member retains the spring in the cylinder. The pusher member is coupled to the body portion by a first locking pin which passes through the pusher member and the slots of the cylinder. The first locking pin slidingly engages the longitudinal slots to allow the pusher member to come into contact with the spring. When a force greater than the static spring force is applied to the pusher member, the pusher member retracts into the body portion thus reducing the overall height of the pusher dog.
A conventional power and free conveyor system comprises a powered drive chain spaced horizontally parallel above a non-powered free rail. In particular in the clothing industry, articles of clothing are suspended from load carriers which move freely upon the non-powered free rail. The powered drive chain comprises a plurality of pusher dogs to continuously move the load carriers throughout the system.
An advantage to the self-actuating retraction of the subject invention is realized when a system comprises many branches leading into a main rail. When one powered system in harddog mode is automatically feeding load carriers to another powered system in harddog mode, damage may result if the timing of the two systems is off. With the new and improved retractable pusher dog, jamming of load trolleys will be prevented by allowing the pusher member to bypass an off-timed load carrier until it is properly aligned on the main rail. In the same sense, binding and breaking of trolleys will be avoided when manually feeding load carriers onto a powered system in harddog mode.
Another advantage of the new and improved retractable pusher dog of the subject invention is the versatility it gives conveyor system designers. For example, when designing inclines, care must be taken to ensure proper alignment between the powered rail and the free rail. If a rigid pusher dog comes into contact with the free rail, undue stress will be placed on the rails and its supporting structure. If the pusher dog of the subject invention comes into contact with the free rail, it will retract upon itself resulting in no stress or strain upon the rail system. This feature gives system designers flexibility in designing steep gradients and such.
The body plates of the pusher dog facilitate coupling the subject invention to the drive chain of the powered rail. The end of the body plate opposite the end positioned on the rectangular cylinder is formed in a xe2x80x9cCxe2x80x9d shape. This C-shaped end engages a center link of the drive chain and is fixed by a locking plate. This coupling feature of the subject invention permits pusher dogs to be installed or replaced without disassembling the drive chain thus reducing downtime and labor costs. This feature also allows the subject invention to be retrofitted onto many types of existing power and free conveyors.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.